Isotope separation process



YFel. 10, 1948. A. F. REID 2,435,795

ISOTOPE SEPARATION PROCESS Filed May 4, 1944 J NOR/ML co2 Patented Feb. 10, 1948 UNITED STATES APATENT YOFFICE Iso'roPESEPARA'IINIRooltss. Alien Francis Reid, New York, N. Y.

Application May 4, 1944,A Serial No. 534,023

s claims; (onza-150) 'Ihis invention relates to the concentration: of isotopes and particularly to the isotopes of carbon and oxygen.

The object of the invention is to relatively increase the concentration of a carbon or an oxygen isotope and involves heterogeneous catalyzed chemicalexchange reactions betweenV Ycarbon dioxideycarbonic `acid,ibicarbonate ion and Water. TheY carbon and oxygen are Vthen distinguishable bythe-'relative `isotopic concentration and may be used asisotopictracers and for other purposes in the study of Ycarbon and oxygen and in quantitive analysis and other reactions.

'In the accompanying drawing illustrating the invention Fig. 1 is a diagrammatioview of av column adapted for theconcentration of`- the isotope C12, and

Fig. 2 is a similar view of a columnfor 4concentration of C13. n

Referring tothe' systemshownv in Fig. l, a vertical container or tower 5 is packed in any desired manner with material. The column is then lled with CO2 forin-stance through supply 1 at the bottom, and a base solution is introduced at the top reactingwiththe'COz to form HCOsn which travels down thecolumn. Normal CO2 is fed in at 'l at constant pressure. Since the heavier carbon concentrates in the liquid zphase, the C12 is concentrated at the top and a; small For a practical `increase in concentration of'an isotope use is made of a system, such as a fractionating column, involving reux over extended surfaces suchA as a number of plates. In surh a of the-slow reaction, or both. As previously noted,

percentage of the CO2 enriched in C12 is bled olt at the outlet 8 at the top of the column,- At the outlet 9 at the bottom there is a steady draining out of bicarbonate solution.

' Normally and without catalysis there are `competing rate controlling reactions:

(1) CO2 (dissolved) :if OH (z H003- (2) f O02 (dissolved) '+1H2O -g H1003 liquids. The exchangereactions are (3) C1102 (gas) -l- [1H2Q12Oz -i- (1-z)HC.12Os-]= insolution c1202 (gas) ameno? (innowo-l in solution (4) oozw (gas) 2112012 1iquid =oo2u (gas) 213201@ (liquid) both (3) and `(4) resulting in afractionation factor vsuitable for` isotopic concentration: at; mod'-l erately low temperature.

Where the rate of the reaction has been speeded up sufficiently the mixing and diffusion factors become determinative.

In the present system the factors involved in the operation include a. A -pressure of CO2A increased preferably above 6 atmospheres givinga corresponding increase in the concentration ofthe CO2 (dissolved) b, A pH sufficiently high so that advantage may be taken of the catalyzed Reaction 1 c. A gas flow of suiicient velocity forl turbulence to increase the mixing and diffusion rates d. As high a temperature as is necessary to keep the catalyzed rates of Reactions 1 and 2 great enough so that they are not rate controlling. The upper temperature limit will be dictated by practical considerations and by the lowering of vthe fractionation factor per plate as thisY decreases with increasing temperature. e. An effective and practical packing witheicient fractionating characteristics and suiiicient catalytic activity sothat the Reactions 1 and 2 are not rate controlling.

The following may be taken as expressing the conditions of isotopic exchange in packed colwhere Ic is a constant; C is the concentration in moles per unit volume of carbon in the liquid; N

= isthe mole fraction of heavy carbon in the liquid;

H is the moles of holdup per unit length of oombined light and heavy carbon in the liquid; L is the ilow of light and heavy carbon in the liquid in moles per unit time; and where lower case symbols designate the corresponding quantities in the gas phase, z is the distance along the column measuredA fromthe reflux end, and at equilibrium:

3 y Inspection of (6) and (7) indicates at once that for any given column the highest fractionation is obtained with the highest value of kcC. However, that factor is an exchange rate constant per unit 4 The system of this invention thus provides a practical and inexpensive source of concentration of oxygen and carbon isotopes. The tortuous passages through the packed column impart a length of column, and as such varies from column 5 turbulence to the gas phase of .the exchange and to column with the cross-sectional area, so that desired pressures may be readily attained. The the exchange rate per unit Volume of packing, materials used are readily available and the sysirrespective of the size of the particular column tem does not involve any poisonous substances or used turns out to be lccC/A, where A is the crosshazardous conditions of operation. sectional area, and is the quantity to be maxl I Clalm! imized. v1. A process of relatively concentrating isotopes The value of a (alpha) will be taken as 1.012. of carbon and of oxygen comprising reacting car- The following runs are typical of results atbon dioxide with carbonio acid, bicarbonate ion tained at room temperature: and water under pressure from 6 to approximate- Flowmoles kcC/A Preiiure Base used per plncf Atmos' minlxlO-ii per min.

Packinge'tchedsiiiceousshaie' o 2.3M Nmon..- 15.4 1o.5x1o'` 6-8 mesh. Do 1e 10.1 35.4 1o- 9S" iPyrex helices etched 23 18 2.6M NHiOH.-. 17.3 38Xl0 l1 mD o 2.5M NHloH--- 1e 4 40 10 The etching was with 8.4% HF so1ution, and 1y 50 atmospheres at room temperature to apsiliceous packing thus etched was satisfactory. proximately 64 C. in the presence of a hetero- The siliceous shale packing had suincient catageneous catalyst packing Ycontamina a member lytic activity and good fractionating characterof the group consisting of silicon oxide, a silicate, istics. The Pyrex helices similarly etched also carbon and aluminum oxide and ilowing carbon showed easily suiiicient catalytic activity and dioxide into the solution of carbonio acid and somewhat better fractionating characteristics. bicarbonate ion at a rate above 15 millimoles per Activated charcoal (Morell Char. No. 7) and sq. cm. per minute to give a substantial relative A1203 have sufficient catalytic activity when fresh. isotopic concentration, continuing said reaction Corning Fiber Glass No. 9930 and other catalysts to change the concentration or the isotopes of are also effective as indicated in the following carbon and oxygen, and bleeding off from the data from runs in small reaction vessels filled heterogeneous catalyst a uid enriched with the with the packing moistened with the liquid phase desired isotope. filled with the gas phase and allowed to stand 2. Aprocess of relatively concentrating an elefor a limited length of time: 40 ment as set forth in claim 1 comprising reacting n10/[Axle: 11109500.1311. Packing Solution Tglp" Pressre 11a/in.'

exchange exchange Calcined silica gel H2O, 0.111% H2Ou 25 765 69 20% Pbooi on Alion... dn 23 765 4o Do dn e4 765 so Aigo., 15.2% Hgo do 2s 765 14o Do 2.1 M KHCO., 4.7% KHcoo 29 765 Morell Char. No.7 H2O, 0.111% H2O!8 23.5 765 351 A: Corning Fiber Glass No. 2.1MKHCO3, 4.7% KHCliOa 26 765 This system of accelerating the C and O isotope concentration is practical and inexpensive. The materials are commonly available, nonpoisonous and the reactions are not complicated or coupled with any undesirable results.

The column of Fig. 1 is,l shown operative for packed column 5' as the CO2 gas from the lower reux I6 progresses upward through connector 20 to the column and the upper discharge outlet at 2 l. Acid supplied to the reflux reacts with the bicarbonate solution to give the CO2 a small percentage of Which enriched in C13 is drawn oii at the lower outlet l1.

the carbon dioxide, carbonio acid, bicarbonate ion and water in the-presence of aluminum oxide as a heterogeneous catalyst.

3. A process of relatively concentrating an isotope of carbon'and oxygen comprising reacting carbon dioxide with carbonio acid, bicarbonate ion and water under pressure above atmosphere at room temperature to approximately 64 C. in the presence of a catalyst of a group of materials heterogeneous with respect to the reactants and containing a member of the group consisting of silicon oxide, a silicate, carbon, and aluminum oxide at a pH of 5 or over to give a substantial relative isotopic concentration. continuing said reaction to change the concentration of the isotopes of carbon and oxygen, and bleeding on a fluid enriched with the desired isotope.

4. A process of relatively concentrating an isotope of carbon and oxygen as set forth in claim 3 comprising reacting carbon dioxide and the water solution of carbonio acid and bicarbonate ion under pressure ranging from 6 to aptration of the isotypes of carbon and of oxygen i and bleeding oi from said catalyst a fluid enriched with the desired isotope.

6. A process of relatively concentrating isotopes of carbon and of oxygen comprising reacting carbon dioxide with carbonio acid, bicarbonate ion and water by owing carbon dioxide upward counter current into a descending solution of carbonio acid and bicarbonate ion at a suiiicient Velocity for turbulence to increase the mixing and diiusion rates and at moderately low'temperature above room temperature in the presence of a heterogeneous catalyst packing containing a member of the group consisting of silicon oxide, a silicate, carbon and aluminum oxide to give a substantially relative isotopic concentration, continuing said counter current reaction to change the concentration of the isotopes of carbon and bleeding off CO2 enriched in C12 from the heterogeneous catalyst at the upper portion of the counter current exchange.

'7. A process of relatively concentrating isotopes of carbon and of oxygen comprising reacting carbon dioxide with carbonio acid, bicarbonate ion and water by flowing carbon doxide upward countercurrent into a descending solution of carbonic acid and bicarbonate ion at a sufcient velocity for turbulence to increase the mixing and diffusion rates and at moderately low temperature above room temperature in the presence of a heterogeneous catalyst packing containing a member of the group consisting of silicon oxide, a silicate, carbon and aluminum oxide to give a substantially relative isotopic concentration, continuing said countercurrent reaction to change the concentration of the isotopes of carbon and bleeding off CO2 enriched in C13 from the heterogeneous catalyst at the lower portion of the countercurrent exchange.

8. A process of relatively concentrating isotopes of carbon and of oxygen which comprises passing into countercurrent contact ammonium bicarbonate water solution and carbon dioxide under a pressure from 6 to approximately 50 atmospheres at a temperature within the range of from room temperature to about 64 C, in the presence of a hetergeneous catalyst packing containing a member of the group consisting of silicon oxide, a silicate, carbon and aluminum oxide, the carbon dioxide in said countercurrent contact being fed at a rate above about 15 millimoles per square centimeter per minute and sufficient for turbulence to increase the mixing and diffusion rates and to cause a substantial relatively isotopic concentration continuing said countercurrent contact to change the concentration of the isotopes of carbon and oxygen and bleeding off from the reaction zone a fluid enriched with the desired isotopes.

ALLEN FRANCIS REID.I

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Name Date Hansgirg May 2, 1939 OTHER REFERENCES Number 

